Production of magnetic material



Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE am-saessm s is:

assignments, to Radio Corporation of America, New York, N. Y.. acorporation of Delaware No Drawing.

Application April 26, IQS'L'SQI'III No. 139,000. Iii Germany April 29,1938 SCIaims.

It is common to produce magnetic cores for intermediate and highfrequency purposes from finely powdered magnetic material, such as ironor ferromagnetic alloys, by compressing the particles by means of abindingagent to form a solid material. For the purpose of avoidingconductive relative contact between the'said particles, various methodshave been proposed according to' thereto, a film of a phosphoric acidmetal compound is mounted on the magnetic particles without theseparticles assisting genetically in the tack of the surface since therate and the uniiormity of the chemical attack per particle canonly becontrolled with difiiculty. The fact that in accordance with theinvention no gas development as a result of chemical reaction arises isalso conducive to uniformity.

The invention is consequently particularly adapted for use with magneticparticles the di-- mensions of which are in the order of magnitude to afew a, the thickness of the insulating films to be obtained notexceeding20 ma. 0

Since in accordance with the invention the magnetic particles have beenprovided with a thin insulating film, the magnetic powder thus obtainedcan be given any shape by compression. I

In order to increase the mechanical strength of the magnet core abinding agent may be used with advantage in a manner known per se afterthe insulating film is mounted. For this purpose, use may be made, forexample, of a synthetic resin which may be capable of being hardened.

In the use of a resin capable of being hardened.

even distribution of the magnetic particles in the final product may beassisted by grinding the material after mixture ,with the resin, by nextgiving it at ordinary temperatures the desired shape and by then heatingit to cause it to harden.

Example I I 1 kg. of magnetic powder is introduced into 1 litre of a 2normal solution of aqua-ammonia containing 60 milliequivalents of zincion and 60 milliequivalents of phosphate ion. The excess of aqua-ammoniais then removed by boiling while shaking continuously so that all thezinc phosphate present in the solution is precipitated on the surface ofthe particles. After being filtered and dried, the powder is squeezedinto the desired shape at a pressure of about 5000 kgJcm.

zinc ion and 45 milliequlvalents of phosphate ion per 100 cm. The pastethus obtained is kneaded while evaporating the excess of aqua-ammoniaand water, which may be efi'ected while heating.

to a low extent or in vacuo at ordinary temperatures. The material isthen completely dried and ground to form a powder which is mixed with analcohol solution containing 60 grams of a hardening phenoli'ormaldehydecondensation product. Alter volatilisation of the solvent the powderlngoperation is renewed and the powder is then squeezed at 150 C. into thedesired shape, it being possible to apply a squeezing pressure of 1500k8./cm.

In order to avoid the presence of other electrolytes which would affectthe properties of the core, the ammoniacal zinc phosphate solution maybe obtained by newly precipitated zinc hydroxidebeing dissolved in aconcentrated solution of aqua-ammonia, by a dilute phosphoric 1 kg. ofmagnetic powder is intimately mixed with about 100 cm. of a weakly-acidferric phosphate solution containing 30 mllliequivalents of ferri-lonand milliequivalents of phosphate 7 tained is reduced to the form of apowder and mixed with an acetone solution containing grams of thecommercial resin known under the registered trade mark "plastopal H.Alter volatilisation of the solvent, the material is squeezed into thedesired shape at ordinary temperatures, it being possible to apply apressure of 5000 kg./cm.

1 kg. of magnetic powder is intimately mixed with about 100 cm. of a 2normal solution of aqua-ammonia containing 30 milliequivalents ofcupri-ion and 45 milliequivalents or phosphate ion per 100 cm. and themixture is evaporated to dryness and powdered, while-kneading, in themanner described in the second example. The powder is agitated in asolution containing grams of a hardening phenolformaldehyde condensationproduct and is then evaporated to dryness while shaking. The materialthus obtained is reduced to the form of a powder and then squeezed atordinary temperatures at a pressure of about 5000 lrg./cm. The coresthus obtained are hardened in a furnace by heating for three hours at130 C.

The quantities, indicated in the examples described, of the substancesused are chosen to accord with the specific weight of the iron and anaverage size of the particles 01 3 a as possessed by certain knowncommercial powdered iron by means of which the invention yieldsparticularly favourable results.

What we claim is:

1. A process of providing particles of ferromagnetic-metallic materialwith a coating of insulation material substantially entirely byprecipitation of phosphoric acid metal compound from a dispersion whichhas substantially no chemical reaction with the magnetic material itselfwhereby the original size of the magnetic particles is substantiallyunafiected during the process, which consists in intimately mixingcomminuted ferro-magnetic-metallic material with a compound comprisingweakly-acid ferric phosphate solution containing substantially equalmolecular amounts of ferri-ion and phosphateion to form a paste, dryingthe mixture while subjecting it to a kneading action and thereaftercomminuting the resulting material.

2. The process described in the next preceding claim characterized bythat each kilogram of ferro-magnetic-metallic material is mixed withapproximately cubic centimeters of weaklyacid ferric phosphate solutioncontaining 30 milliequivalents of ferri-ion and 30 milliequivalents ofphosphate ion.

3. The steps in a process of providing particles ofIerro-magnetic-metallic material with a coating of insulation materialwhich consist in intimately mixing comminuted ferro-magnetic-metallicmaterial with a compound comprising weakly-acid ferric phosphatesolution containing substantially equal molecular amounts of ferri-ionand phosphate-ion, and drying the mixture while subjecting it tosubstantially continuous agitation.

EVERT JOHANNES WILLEM VERWEIJ. JAN HENDRIK DE BOER. THEODORUS ANTHONIUSSPOOR.

